Purification and Characterization of Two Phytases from Escherichia coli

Two periplasmatic phytases, called P1 and P2, were purified about 16,500-fold to an apparent homogeneity with a recovery of 7 and 18%, respectively. The enzymes behave as monomeric proteins with molecular masses of about 42 kDa. Because of the limited amounts recovered, the amino terminal sequence of only one of the phytases was determined. Both enzymes are very specific for phytate and have little or no activity on other phosphate esters tested. The kinetic parameters for the hydrolysis of Na-phytate and p-nitrophenyl phosphate are kcat/KM 478 ×105 s−1 M−1 and 0.6 · 105 s−1 M−1 at pH 4.5. The hydrolysis pathway for phytate was elucidated for P2; consequently, this enzyme is a 6-phytase. The chemical and kinetic properties of the purified phytase P2 points to an identity with an enzyme described by Dassa et al. (1982, J. Biol. Chem. 257, 6669-6676) as a pH 2.5 acid phosphatase. Because of the kinetic parameters it would be better to denote this enzyme as a phytase.